Opposing history effect of preceding decision and action in the free choice of saccade direction

When we act voluntarily, we make a decision to do so prior to the actual execution. However, because of the strong tie between decision and action, it has been difficult to dissociate these two processes in an animal's free behavior. In the present study, we tried to characterize the differences in these processes on the basis of their unique history effect. Using simple eye movement tasks in which the direction of a saccade was either instructed by a computer or freely chosen by the subject, we found that the preceding decision and action had different effects on the animal's subsequent behavior. While choosing a direction (previous decision) produced a positive history effect that prompted the choice of the same saccade direction, making a saccadic response to a direction (previous action) produced a negative history effect that discouraged the monkey from choosing the same direction. This result suggests that the history effect in sequential behavior reported in previous studies was a mixture of these two different components. Future studies on decision-making need to consider the importance of the distinction between decision and action in animal behavior.